Latex compositions and method of producing porous diaphragms



Jan. 9, 1951 H. w. GREENUP ET AL 2,537,631

LATEX CoMPosI'rIoNs AND METHOD oF PRODUCING PoRoUs DIAPHRAGMS Filed Nov. 29, 1945 INVENTOR. HAROLD WGREENUP AN D VI CTOIQ PREN BY T ATTO/ragga xatenteci `an. 9, 1951:v UNITED STATES PATENT OFFICE LATEX COMPOSITION S AND METHOD OF PRODUCING POROUS DIAPHRAGMS Harold W. Greenup, Barrington, and Victor Malcolm Green, Portsmouth, it. I., assignors to The Firestone Tire & Rubber Company, Akron, Ohio, a corporation of Ohio Application November 29, 1945, Serial No. 631,786

6 Claims. (Cl. 18'-58).

This invention relates to a latex composition, its use in the manufacture of microporous diaphragms which are suitable for use as battery `separators and the like, and the diaphragms thus produced.

The diaphragm of this invention is a modified ebonlte. It is formed by the deposition of latex on a form through any suitable means of coagulation. 'l'he form may, for example, be first dipped into a coagulant and then in the latex composition which constitutes one feature of the invention. ,n

' 'l'he procedural steps are illustrated in the accompanying-drawing. Y Y

The latex composition comprLses one or more extenders whichV impart strength and flexibility to the diaphragm. A mixture of Gilsonite or other hard asphalt and coumaronev or other coumarone-indene-type resin is used for this purpose. The deposited latex is cured under water and is thus made to retain substantiallyall the Water originally present in `the latex gel orcoagulum. This contributes materially to the porosity of the diaphragm. The lat-ex includes starch or other suitable hydrolyzable carbohydrate which hydrolyzes during the underwater cure and is dissolved out of the diaphragm during the cure. This results in an increase in the porosity of the `ebonite product. If this product is to beused as a battery separator, the increase in porosity decreases v.its electrical resistance, a desirable attainment. If, on the other hand, the diaphragm is to be used as a lter plate, the in crease in porosity is, likewise, beneficial.

The latex bath is prepared by mixing several dispersions. A natural-rubber latex of about Y60 per cent concentration is preferred as the basis of the bath. About 40 parts of sulfur are added in the form of a dispersion which is made with any suitable dispersng agent. The sulfur dispersion may, for example, be formed by ballmilling 50 parts of sulfur, 1.5 parts of Daxad No. 27 (a dispersing agent manufactured by Dewey and Almy Chemical Company, of Cambridge, Massachusetts, and described in the literature as compounded substituted benzoic alkyl sulfonic acids), and 0.5 part of commercial aqua ammonia (28 per cent). This dispersion is preferably prepared by ball-rnilling the ingredients with 48 parts of water for about forty-eight hours.A

Any suitable accelerator of vulcanization may be employed. A preferred accelerator isr dbenzothiazyl thiomethylureaiknown in the industry as L-60, produced by Monsanto Chemical Company). A suitable accelerator dispersion is prepared by ball-milling 50 parts of this accelerator with about 1.5 parts of Daxad No. 27 and 48.5 parts of water for about twenty-four hours.

To give the diaphragms the desired porosity, a material which hydrolyzes into one or vmore water-soluble components at the temperature of the cure, and during the cure, is added to the latex. Corn starch, lwhich Vhydrolyzes into dextrin and then glucose, is preferred althoughd other starches andother hydrolyzable carbohydrates, etc., may be used.V The corn starch is` added to the latex as a slurry which may, for example, be formed by mixing with an equal weight of water underhigh-speed agitation for from five to ten minutes. fSeven and one-half to twelve parts of the starch will be used per fifty parts of rubber. No wetting agent or the like is required.

TwoV parts of Zinc oxide are added as a dispersion.` 'ih s may be ioimn by ball-milling for about twenty-four hours 4J parts or zinc oxide, 2 parts of Darvan No. l a dispersing agent sold by R.T. .Vanderbilt Company, of New York, described in the literature as polymerized sodium salts of alkyl naphthalene sulfonic acids), and 58 parts of Water.

The latex is advantageously stabilized, as, for example, by the addition of formalin and potassium hydroxide. Ll0 per cent solution of the formalin may be used,` and the potassium hydroxide isadvantageously added as a 25 per cent solution.-

The extender, which imparts strength and flexibilityrto the diaphragm, may be formed of one Yor more materials. It preferably comprises 121/2 to 30 parts per 50 parts of rubber. Preferably the extender is composed of a mixture of Gilsonite and a coumarone-indeneV resin. (Gilsonite isa hard natural asphaltic material of high melting point.) Any asphalt melting betweenabout 250 and 350 F'. may be substituted for the Glsonite. Gilsonite alone has been employed, but the addition of the coumarone-indene resin gives more ilexibility to the diaphragm. The Glsonite known in the trade as 5. S.

(super select) grade is preferred. The coumarone-indene resin is preferably a high-grade coumarone resin with a melting point of about 230 to 280 The material or materials used as an extender should have a melting point of at least about 225 F.

For instance, a diaphragm prepared as herein more particularly described, but using 50 parts of Gilsonite and no resin, gave a diaphragm somewhat weaker than desired. Various formulae were tried using at least half as much coumarone as Gilsonite. Using 40 parts of Gilsonite and 40 parts cfa coumarone resin to 100 parts of latex (dry weight), a Very porous and .otherwise Very satisfactory separator which had an electrical resistance inthe neighborhood of .06 ohm per square inch was obtained. Using 40 parts of the coumarone resin and parts of Glsonite to 100 parts` of rubber, a good, porous separator was prepared, but the latex was very unstable and coagulatedin twenty-four hours. Rapid coagulamarone resin and GrilsoniteJcontent''19020,partsT of each to 100 parts of rubber, 'a good vs'epar""a.l.or was obtained with a resistance przpilohmkper square inch. The preferred ratio Lis, \l,5.,l.39ls V,of

coumarone resin to 25 parts of .Gilsonita andths is employed in the following latex formula.

For use in the following formula .thelzegtender material Was prepared by ballmilling fort'rvety four hours part-s of coumarone resin, 25 parts of Gilsonite, 0.5 per cent potassium hydroxide, 3 ,Der .Gent Peri/an ',NQ- 1f, 36,5 .parte ,Qf. Water. The latex 119.21111v was. Prepared by: mixing .wives eeuws disperdere .ereparcies abovejdescribed to sive a bath QI the,fellviesompesiiienr Dry basis 60% latex 5; 100.0 40% zinc oxidedispersion 2.0 50% sulfur dispersion 40.0 50%V 1F60 acceleratordispersion .0.5 50% corn starch suspension 20.0 25% potassium hydroxide solution 1.5 40% formalin solution L 1 5.3 50% mixed extender dispersion 40.0

The separators WereV prepared by dippingV the forms into a 40 percent solution of'calcium chloride and then dipping into .the latex'bath. Other coagulating means may be employed. As soon asithe dipped forms hadbeen removed from 'the latex and the latex had set (not'dried) on the outer surfaceabout lour to. ten minutes-lthe coated forms were placed in Water in a steam autoclave and. cured uri-der 120 poundsisteam pressure (350 F.) for forty-five minutes. During the cure the rubber is vulcanized to ebonite, and the starch4 is hydrolyzedfinto Water-soluble materials which aredissolved out of the product. The fact that the rubber is cured under Water under pressure and, therefore, retains the Water originally present in the latex gives it'porosi'ty which is increased by the dissolution and removal of the starch. Battery sepa'ratorsproduced-,in this manner had a resistance of about .045 ohm per square inch.

Instead of thin microporous ebonitek battery separators, lter plates, etc., maybe similarly formed, the only difference in the productsbeing the molds upon which the latex` is deposited l It is not necessary to employ natural latex. Synthetic latices, reclaims, etc., may be similarly einployed to produce ebonite-like diaphragme, using hard asphalts and coumarone-indenetype'resins as extenders to strengthen and lend ilexibility to the diaphragme produced. The conditions of cure may be varied although curing underwater is necessary to produce a microporous product of the typehere contemplated."

What We claim is:

1. A mioroporous ebonite diaphragm which comprises' hard rubber formed of 50 parts 'of`rbber vulcanized with `parts of sulfur.' Z1/2 parts coumarone resin with a melting Ypoint of 230 to 280 F., and 121,/2 parts of asphalt melting at 250 to350F.

'2. The method of producing a, microporous ebonite-like diaphragm which comprises depositing on a form a r'ubbery latex 'which entaisl'Q) sucient sulfur to` producean bohitlik'prodduct (`2) v an extender lcomposed largely of aslhelf .'eali; the essentiel.ineredintsof which has a melting point of at least 225 F. which imy parts strength and flexibility to the diaphragm,

vand (V3) cprn starch, and curing the deposit in hot Water while thusv simultaneously hydrolyzing and dissolving outthe starch.

3.@1he AVmetl'ipd ol producing a microporous ebOnte-likedaphragm which comprises deposit- Sing' on a form a rubbery latex Which contains (l) ysufficient sulfur to produce an ebonite-like product, l.(2).` extenders of hard asphalt and coumarone isilt strengthen "the diaphragm and make it exibl'e,'and (3) corn starch, and curing the deposit in hot water While simultaneously hydrolyz- .ire' the ,starhin the .Water to produpetbe microrereils., ebenda-,like diaphragm.

Y.,i. The methpd 9i producing a, micrgpormfls diaphragm ,wbilrsomprises forming on.. a .suitable surfaoe a thin deposit by coagulation kfrom a .Datasemprisine ...5.0 parts natural. latex which has. .dispersediberen 20 partsof Sulfur, -12 .1/2 .to 30 parte ofl liardasphalt and. poumarone, resin which. Astre.n etnens and imparts .flexibility ,ton ...the uisheddapbreem.. and, 7.1/2 to` 412- parts omero starhandptber yulanizine. ineredientsother than sulfur, and thereafter vulcanizing.` the deposit.- .to ebonite underA ,heated `Water vwhich hydrolyzes the starch into Water-soluble decomposiftienrrodutsdurine the .cure- .51 ,The methedjof producing, av microporous ebonte ,battery Separatorwhch .comprises coatine. e Suitable form ,with a coagulantdpping ,the Same .ntor parte of natural rubberlatex ,which has. dispersed. therenzupartssulfur, 71/2 parte resin with.. a. melting. point .of 2.30 to 230 E., 121/2 .parteci asphalt-melting at 250,130 3,59".-

andglparts. ofoornstarcnand thereafter yulcanizing, the deposit underhot water which.. .cures .the A rulolofay and simultaneously. hydrolyZS .the .Starchto Aproduce va microporous @bonita 6. A natural L latex4 composition .which .comprises dispersed thereimby dryv weight, 50 parts rubberoithelatex, 20 Ypartssulfur.,'l1/2 tomi/2 parts ordern.V starch and. 121K; y110,30.partsofan extender;composedY essentiallyof .hard asphalt and at, least `hall? as mnchcoumaronefindene resin aS Sphalt, each,of,.which..ingredients hasa melting point of at ,least.225? F., which extender mpartsstrength andsfle'xibility to thefebonite productobtainedby. coagulation and vulcanize- .tionof the latex composition.

The lfollowing 'references .arabi recordin the 131e, of. this, patent:

lQTHER. REnanNcns 

1. A MICROPOROUS EBONITE DIAPHRAGM WHICH COMPIRSES HARD RUBBER FORMED OF 50 PARTS OF RUBBER VULCANIZED WITH 20 PARTS OF SULFUR, 7 1/2 PARTS COUMARONE RESIN WITH A MELTING POINT OF 230 TO 280* F., AND 12 1/2 PARTS OF ASPHALT MELTING AT 250 TO 350* F. 